Oil rigs are offshore structures that are used to extract petroleum and other naturally-formed hydrocarbon deposits (eg natural gas) from the seabed. However, many oil fields are found in inhospitable locations. These locations may have extreme environmental conditions such as storms and ice at certain times of the year.
To maximize their output or productivity, oil rigs are operated for as long as possible in the window of opportunity afforded by the milder months. This window may be as short as three months in the higher latitudes. When the environmental conditions change for the worse, these rigs may be temporarily abandoned or if they are mobile, displaced to another safer location.
To enable such mobility, oil rigs may be self-propelled or may be towed to the desired site, and anchored. The means of anchoring are well known in the art. These may include legs that reach to the seabed enabled by jacking systems such as in U.S. Pat. No. 6,076,996 and in the oil rigs designed and built by the applicant of the present invention (U.S. Pat. No. 6,030,149). Alternatively, oil rigs may be submersible or semi-submersible by having ballast tanks that may be flooded to anchor the oil rig as exemplified by U.S. Pat. No. 5,292,207.
Besides having to be securely anchored during use, there is the danger posed by ice formations to oil rigs in arctic conditions. Currently, icebreaker ships may be employed to break up ice formation around an oil rig to prevent the ice build-up from damaging the rig. In the case of U.S. Pat. No. 5,292,207 or U.S. Pat. No. 6,371,695, the rigs may possess built-in means or provide a crush-resistant structure against encroaching ice, obviating the need for icebreaker ships.
These built-in ice breaking means are usually heavily sloped plates or plates installed around the support legs of a rig. The idea behind such inventions is that by flexing the ice will cause it to fracture. Thus, as the ice sheet is formed and moves against the rig, the ice sheets slide up the slope of the plate. As the angle of the slope is sharp, the rigid ice sheet does not bend and instead fractures. As such, damage from ice sheets building up around the supporting leg is prevented. In another invention, U.S. Pat. No. 4,102,144, the ice breaking means is raised along the supporting leg to break the ice. The shield may be heated to melt ice pieces adhering to it, dislodging them.
These inventions show that means to anchor an oil rig or similar structure are important, as are means to prevent damage from ice build-up.
Therefore, there is a continued need for means to allow an oil rig or similar structure to operate in harsher environments such as rough seas or icy conditions to tap the hydrocarbon reservoirs in these regions. An invention that can withstand such conditions will extend the window of operation for oil rigs, increase the production capacity while reducing costs, and hence improve the profitability of the rig. Such an invention will be welcome in the industry.